EP0440491A1

EP0440491A1 - Vibration wave driven motor

Info

Publication number: EP0440491A1
Application number: EP91300802A
Authority: EP
Inventors: Akio C/O Canon Kabushiki Kaisha Atsuta
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1990-02-02
Filing date: 1991-01-31
Publication date: 1991-08-07
Anticipated expiration: 2011-01-31
Also published as: US5134333A; JPH03230771A; EP0440491B1; JP2669916B2; DE69108946D1; DE69108946T2

Abstract

This invention relates to a vibration type motor in which frequency signals differing in phase from each other are applied to an electro-mechanical energy conversion element disposed on a vibration member to thereby vibrate the vibration member and drive a movable member by the vibration force. This invention provides a motor of the described type in which a monitoring portion for detecting the vibrated state of the vibration member is provided at a location avoiding a location at which the rigidity of the vibration member exhibits rigidity differing from the rigidity of the entire vibration member so that the vibrated state can be accurately detected.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a vibration type motor in which a vibration member and a member which is in contact with the vibration member are moved relative to each other by vibration generated in the vibration member.

Related Background Art

Figure 6 of the accompanying drawings shows the electrode arrangement of a piezo-electric element provided on the resilient member of a circular ring-shaped vibration wave driven motor according to the prior art. As shown, two groups of electrodes [A phase (A₁-A₆) and B phase (B₁-B₆) having a pitch of 1/2 of the wavelength of a vibration wave excited in a circular ring-shaped vibration member are spatially disposed with a pitch 1/2, i.e., with a phase deviation of 1/4 of said wavelength, and a sensor electrode S for detecting the vibrated state of the circular ring-shaped vibration member, i.e., an electrode such as a piezo-electric element generating an electromotive voltage by the vibration of the vibration member, and common electrodes C (C₁, C₂ and C₃) are further provided between these two groups of electrodes. The vibration member comprises a resilient member of a metal or like material and a piezo-electric element (e.g. PZT) as an electro-mechanical energy conversion element attached to the resilient member, and the associated electrode of the electro-mechanical energy conversion element which is adjacent to the resilient member is short-circuited through the metallic resilient member. The common electrodes C₁, C₂ and C₃ are rendered conductive with the resilient member by an electrically conductive paint or the like, and the potential difference from the resilient member is zero. When a potential of a certain magnitude relative to the potential of the common electrodes C is input to driving electrodes A₁-A₆ and B₁-B₆, a potential difference is produced between the front and back of the electro-mechanical energy conversion element and strain is created. Signs - and + shown on the electrodes indicate the directions of polarization of the piezo-electric elements in the electrode portions.
By a voltage V=Vo sin ωt being applied to the group of A phase electrodes A₁-A₆ and a voltage V=Vo sin (ωt ± $\frac{π}{2}$
) being applied to the group of B phase electrodes B₁-B₆, a travelling vibration wave is generated in the resilient member and a conventional movable member (not shown) such as a rotor which is in pressure contact with the resilient member is moved by friction. Also, by changing the signs (+) and (-) in the aforementioned equation, i.e., advancing or delaying the phase of one of the applied voltages with respect to that of the other, it is possible to change the direction of movement of the movable member, and in the case of (-), i.e., where a frequency voltage delayed in phase by $\frac{π}{2}$
(90°) with respect to the frequency voltage applied to the A phase is applied to the B phase, the movable member is rotated clockwise (CW), and in the case of (+), i.e., where a frequency voltage advanced in phase by $\frac{π}{2}$
(90°) with respect to the frequency voltage applied to the A phase is applied to the B phase, the movable member is rotated counter-clockwise (CCW).
A signal detected from the sensor electrode S is a signal having a certain phase relation with the frequency voltage applied to the A phase when the movable member is in a resonance state, but it becomes a signal deviating from said certain phase relation with the frequency voltage applied to the A phase when the movable member is in a non-resonance state. So, by detecting the phase difference between the driving voltage and the detection signal, it is possible to know whether the vibration is in a reasonance state of great amplitude or how much the vibration deviates from a resonance state, and by determining from this information the frequency to be applied, the control of the rotational speed is possible.
Figure 7A of the accompanying drawings is a fragmentary cross-sectional view of the resilient member of the vibration wave driven motor. A piezo-electric element 2 as an electro-mechanical energy conversion element is attached to the resilient member 1 of Figure 7A. Symbols below the element 2 represent the positions of the electrodes of Figure 6. A number of grooves each having a width t₁ and a depth h₁ are formed in the surface of contact of the resilient member with the rotor (not shown) over the entire circumference thereof. Some of these grooves are deep grooves of a depth h₂ to prevent the creation of noise.
The spacing between the deep grooves of Figure 7A may be suitably selected, but if this spacing is 60°, the vibration of the 3rd-order mode can be suppressed. As described above, the arrangement of the deep grooves gives birth to the effect of suppressing a single or a number of modes of noise and preventing noise.
At this time, the electrode pattern of the piezo-electric element which is an electro-mechanical energy conversion element and the pattern of said deep grooves are arbitrarily positioned.
In the case of the combination of the sensor electrodes S and the deep groove pattern as shown in Figure 7A, the deep groove portion is near the sensor electrode S, and as shown in Figure 7B of the accompanying drawings, the rigidity of the portion of the sensor electrode S varies. At this time, there is obtained the relation of the frequency f vs. the phase difference ϑ_A-S between the A phase and S phase as shown in Figure 8 of the accompanying drawings. When the frequency of the resilient member is a resonance frequency, the phase difference ϑ_A-S is -135° for CW and -45° for CCW.
However, since the rigidity of the portion near the sensor electrode S varies as shown in Figure 8, the amplitude and wavelength of the travelling vibration wave change delicately, and the CW rotation and the CCW rotation deviate from each other in opposite directions with respect to the ideal f vs. ϑ_A-S curve (the portion indicated by dotted line in Figure 8).
Consequently, there is the problem that a right resonance frequency is not detected even if the ϑ_A-S phase difference is adjusted to -135° (for CCW, -45°). That is, in the example of the prior art described above, if the positional relation between the electrode pattern of the piezo-electric element which is an electro-mechanical energy conversion element and the deep groove pattern of the resilient member is arbitrary, the portion in which the rigidity of the deep groove portion varies is disposed near the sensor electrode S as shown in Figure 7B, and this adversely affects the signal of the sensor electrode S and thus, a difference occurs relative to the true f vs. ϑ_A-S curve, as shown in Figure 8. That is, near the deep grooves, strain differs and the center of the electrode for a sensor becomes as if it deviated and thus, it follows that a right resonance frequency is not detected.

SUMMARY OF THE INVENTION

One aspect of the application is to solve the above-noted problem peculiar to the prior art and to provide a vibration type motor in which a sensor electrode always enables the detection of a right resonance frequency.
One aspect of the application is to provide a vibration type motor in which an electro-mechanical energy conversion element having at least a driving electrode and a vibration detecting electrode is disposed in a single layer a plurality of layers on a resilient member and frequency voltages differing in phase from each other are applied to the driving electrode to generate a travelling vibration wave, whereby said resilient member and a member which is in pressure contact with said resilient member are moved relative to each other, and wherein said vibration detecting electrode is disposed at the center of that portion of said resilient member in which the rigidity of said resilient member varies, or avoiding that portion in which the rigidity of said resilient member varies.
One aspect of the application is to provide a vibration type motor in which an electro-mechanical energy conversion element is disposed on a vibration member and a frequency signal is applied to said element to vibrate said vibration member and the vibration force of said vibration member is used as a drive force and wherein a sensor electrode for detecting the vibrated state of the motor is disposed in a portion wherein the variation in the rigidity of the vibration member is small or a portion wherein the variation in the rigidity of the vibration member occurs symmetrically with respect to the sensor electrode, whereby the vibration state of the motor is made accurately detectable.
Other objects of the present invention will become apparent from the following detailed description of some embodiments of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows Embodiment 1 of a vibration wave driven motor according to the present invention, Figure 1A being a fragmentary cross-sectional view of a resilient member, and Figure 1B being a graph showing the relation between the position and rigidity of the resilient member.
Figure 2 is a graph showing the f vs. ϑ_A-S relation of Embodiment 1.
Figure 3 shows Embodiment 2, Figure 3A being a fragmentary cross-sectional view of a resilient member, and Figure 3B being a graph showing the relation between the position and rigidity of the resilient member.
Figure 4 shows Embodiment 3, Figure 4A being a fragmentary cross-sectional view of a resilient member, and Figure 4B being a graph showing the relation between the position and rigidity of the resilient member.
Figure 5 is a plan view of a resilient member showing Embodiment 4.
Figure 6 shows the electrode arrangement in a vibration wave driven motor according to the prior art.
Figure 7 shows the vibration wave driven motor according to the prior art, Figure 7A being a fragmentary cross-sectional view of a resilient member, and Figure 7B being a graph showing the relation between the position and rigidity of the resilient member.
Figure 8 is a graph showing the f vs. ϑ_A-S relation in the example of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

Figure 1 shows Embodiment 1 of a vibration type motor according to the present invention, Figure 1A being a fragmentary cross-sectional view of a piezo-electric element 2 and a resilient member 1 near a sensor electrode S, and Figure 1B being a graph representing the rigidity at the same position. The disposition of the piezo-electric element and electrodes is similar to that shown in Figure 6.
Referring to Figure 1A, the resilient member 1 is formed with first grooves 3 each having a width t and a depth h_1. Also, deep grooves 4 each having a depth h₂ are formed in some of these grooves 3. As shown in Figure 1B, the rigidity of the resilient member 1 varies near the deep grooves 4. However, the sensor electrode S is disposed avoiding the deep grooves 4 and therefore, the rigidity of the resilient member 1 is uniform.
Here, the frequency (f) vs. phase difference ϑ_A-S curve of a sensor signal obtained from the sensor electrode S when a voltage V=Vo sin wt is applied to driving A phase electrodes A₁-A₆ and a voltage V=Vo sin (ωt ± $\frac{π}{2}$
) is applied to driving B phase electrodes B₁-B₇ is as shown in Figure 2. That is, it is seen from Figure 2 that the phase difference ϑ_A-S at a regular resonance frequency fr has a difference of 90°, i.e., -135° in the case of CW rotation and -45° in the case of CCW rotation, but the frequency f vs. phase difference ϑ_A-S curve coincides at all frequencies.
By the sensor electrode S being disposed avoiding the portion in which the rigidity of the resilient member 1 varies as described above, the resonance frequency can be detected rightly. Empirically, it is desirable that the amount by which the portion in which the rigidity varies is avoided be λ (wavelength)/4 or more from the portion in which the rigidity is lowest (or highest). Also, where the sensor electrode S is disposed at the center of the portion in which the rigidity varies, it is desirable that said amount be λ (wavelength)/8 or less.
That is, if the sensor electrode is disposed at the center of the portion in which the rigidity varies, as indicated at a position S′ in Figure 1, the vibration state can be accurately detected because the variation in the rigidity occurs symmetrically with respect to the sensor electrode.

Embodiment 2

Figure 3 shows Embodiment 2 of the present invention, Figure 3A being a fragmentary cross-sectional view of a piezo-electric element 2 and a resilient member 1 near a sensor electrode S, and Figure 3B being a graph representing the rigidity at the same position.
Referring to Figure 3A, the resilient member 1 is formed with grooves 3 each having a width t and a depth h₁. Also, grooves 5 each having a depth h₁ and a width t′ and grooves 6 each having a depth h₂ and a width t′ are formed in some of these grooves 3. As can be seen from Figure 3B, the area in which the rigidity of the resilient member varies is decreased by providing the grooves 5 and 6 having the width t′ and the depths h₂ and h₁, and the sensor electrode S can readily avoid the portion in which the rigidity varies.

Embodiment 3

Figure 4 shows Embodiment 3 of the present invention, Figure 4A being a fragmentary cross-sectional view of a piezo-electric element 2 and a resilient member 1 near a sensor electrode S, and Figure 4B being a graph representing the rigidity at the same position.
Referring to Figure 4A, the resilient member 1 is formed with grooves 3 each having a width t and a depth h₁. Also, shallow grooves 7 each having a depth h₃ are formed in some of these grooves 3.
In Embodiment 1, the rigidity is varied by deepening some of the grooves, whereas in the present embodiment 3, the rigidily is varied by making the grooves 7 shallow.
The method of varying the rigidity of a portion of the resilient member 1 to thereby prevent the generation of noise can also be realized by attaching or removing a certain mass to or from a portion of the resilient member. Again in such cases, there exists a portion in which the rigidity varies and therefore, as in Embodiment 1, the sensor electrode S need be disposed avoiding that portion.

Embodiment 4

Figure 5 shows Embodiment 4 of the present invention. In the present embodiment, grooves 8, 9 and 10 are at unequal pitches and the deep grooves 8 painted out in the figure are continuous at a unit of two. In Figure 5, the rigidity of the resilient member varies most in the portions wherein two deep grooves 8 are continuous, and the sensor electrode S avoids particularly those portions. Also, it is desirable that the sensor electrode S be disposed avoiding the portions in which the deep grooves 8 and 10 are provided at one location each.
Each of the above-described embodiments is a circular ring-shaped resilient member, but the resilient member can also be made similar in a case where vibration detecting means is provided for a disk-shaped or linearly shaped resilient member. The number of the piezo-electric element which is an electro-mechanical energy conversion element is not limited to one, but piezo-electric elements may be provided in multiple layers.
As described above, according to the present embodiment, the vibration detecting electrode is disposed avoiding the portion in which the rigidity of the resilient member varies, whereby the characteristic of the phase difference between the output of the vibration detecting electrode and the applied voltage can accurately catch the resonance frequency and can stably drive the motor.
The embodiments are shown as the type in which a travelling vibration wave is formed, but the present invention can be applied to any type in which a vibration member is vibrated by a piezo-electric element and a movable member is driven by the vibration of the vibration member.

Claims

A vibration type motor including:
(a) a vibration member;

(b) an electro-mechanical energy conversion element portion provided on said vibration member, a frequency signal being applied to said element portion to thereby vibrate said vibration member and form a drive force by said vibration; and

(c) a monitoring portion for detecting the vibrated state of said vibration member, said monitoring portion being disposed at other location than that portion of said vibration member in which the rigidity of said vibration member varies.
A vibration type motor according to Claim 1, wherein said vibration member has a physical characteristic varying portion differing in shape, weight or the like from the other portions, and said monitoring portion is disposed in an area avoiding said varying portion.
A vibration type motor according to Claim 2, wherein said monitoring portion is comprised of a signal forming element portion provided on said vibration member for forming an electrical signal conforming to the vibration of said vibration member, and a detecting electrode provided on said element portion.
A vibration type motor according to Claim 3, wherein said signal forming element portion is a part of said energy conversion element portion.
A vibration type motor according to Claim 1, wherein said vibration member is formed with a plurality of slits or projected portions, some of said slits or projected portions differing in shape from the other slits or projected portions, and said monitoring portion is disposed in an area avoiding said slits or projected portions differing in shape.
A vibration type motor including:
(a) a vibration member formed with a plurality of slits or projected portions, some of said slits or projected portions differing in shape from the other slits or projected portions;

(b) an electro-mechanical energy conversion element portion provided on said vibration member, frequency signals differing in phase from each other being applied to said element portion; and

(c) a monitoring portion provided on said vibration member, said monitoring portion being disposed at a location avoiding said slits or projected portions differing in shape.
A vibration type motor according to Claim 6, wherein said monitoring portion is comprised of a signal forming element portion provided on said vibration member for forming an electrical signal conforming to the vibration of said vibration member, and a detecting electrode provided on said element portion.
A vibration type motor according to Claim 7, wherein said signal forming element portion is a part of said energy conversion element portion.
A vibration type motor according to Claim 6, wherein said some slits or projected portions each have a slit length or a projection length differing from that of the other slits or projected portions.
A vibration type motor including:
(a) a vibration member formed with a plurality of slits or projected portions at predetermined intervals, some of said slits or projected portions being disposed at intervals differing from the intervals of the other slits or projected portions;

(b) an electro-mechanical energy conversion element portion provided on said vibration member, frequency signals differing in phase from each other being applied to said element portion; and

(c) a monitoring portion provided on said vibration member, said monitoring portion being disposed at a location avoiding the slits or projected portions disposed at said different intervals.
A vibration type motor according to Claim 10, wherein said monitoring portion is comprised of a signal forming element portion provided on said vibration member for forming an electrical signal conforming to the vibration of said vibration member, and a detecting electrode provided on said element portion.
A vibration type motor according to Claim 11, wherein said signal forming element portion is a part of said energy conversion element portion.
A vibration type motor according to Claim 1, wherein said electro-mechanical energy conversion element is a piezo-electric element.
A vibration type motor according to Claim 6, wherein said electro-mechanical energy conversion element is a piezo-electric element.
A vibration type motor according to Claim 10, wherein said electro-mechanical energy conversion element is a piezo-electric element.
A vibration type motor including:
(a) a vibration member;

(b) an electro-mechanical energy conversion element portion provided on said vibration member, a frequency signal being applied to said element portion to thereby vibrate said vibration member and form a drive force by said vibration; and

(c) a monitoring portion for detecting the vibrated state of said vibration member, said monitoring portion being disposed at the position of the central portion in which the rigidity of said vibration member varies.
A vibration type motor according to Claim 16, wherein said vibration member has a physical characteristic varying portion differing in shape, weight or the like from the other portions, and substantially the center of said monitoring portion is disposed in an area coincident with the center of said varying portion.
A vibration type motor according to Claim 17, wherein said monitoring portion is comprised of a signal forming element portion provided on said vibration member for forming an electrical signal conforming to the vibration of said vibration member, and a detecting electrode provided on said element portion.
A vibration type motor according to Claim 18, wherein said signal forming element portion is a part of said energy conversion element portion.
A vibration type motor according to Claim 16, wherein said monitoring portion is disposed at a location whereat said rigidity varies symmetrically with respect to said monitoring portion.
A vibration type motor according to Claim 16, wherein the center of said monitoring portion is disposed substantially in coincidence with the center of the variation in said rigidity.
A vibration type motor according to Claim 20, wherein said monitoring portion has detecting electrode disposed at a location whereat said rigidity varies symetrically with respect to said electrode.
A vibration type motor according to Claim 21, wherein said monitoring portion has a detecting electrode, the center of which is disposed substantially in coincidence with the center of the variation in said rigidity.
A vibration wave motor having a vibrating member and a sensor, mounted on the vibrating member, for detecting vibrations of the vibrating member, the vibrating member having at least one portion of non-uniform rigidity,
characterised in that the sensor is mounted at the or a said portion and is positioned so that the variation in rigidity in the said portion is symmetrical about the position of the sensor.
A vibration wave motor having a vibrating member and a sensor, mounted on the vibrating member, for detecting vibrations of the vibrating member, the vibrating member having at least one portion of non-uniform rigidity and at least one portion of uniform rigidity,
characterised in that the sensor is mounted at the or a said portion of uniform rigidity.